The present invention relates to polarizers for satellite antenna systems. More specifically, the invention relates to light weight parallel plate polarizers for satellite antenna systems.
Modern communications networks carry immense amounts of information, typically divided for transmission purposes into individual data channels. Whether the data channels carried by the communications network have their origin in the telephone system, television stations, or other source, these data channels often need to be transmitted through a communications network including a satellite link.
A satellite link in a communications network typically carries multiple antennas capable of transmitting wide bandwidth transmitted beams. Each transmitted beam, for example, may be assigned to a particular frequency band in order to reduce co-channel and adjacent channel interference (collectively "interference") which may limit the total bandwidth capacity of each transmitted beam.
Co-channel interference is interference generated in a transmitted beam assigned to a particular frequency band by nearby transmitted beams assigned to the same frequency bands. Co-channel interference occurs even though spot beams assigned to a particular frequency band are physically separated. In part, the amount of co-channel interference depends on the number of nearby spot beams covering the same frequency band.
Adjacent channel interference is interference generated in a spot beam assigned to a particular frequency band by neighboring spot beams of other frequencies. One common cause of adjacent channel interference is imperfections in the antennas used to generate the spot beams. Because virtually all antennas generate frequency sidelobes, the spot beams are not perfectly confined to their assigned frequency bands. As a result, spot beams may spill over in frequency into neighboring spot beams and cause adjacent channel interference.
In the past, satellites have used polarizers on their antennas to help reduce the effects of interference. Polarizers are typically mounted over the output section of an antenna, for example, over a slotted array waveguide. The transmitted beams generated by the antenna then pass into the polarizer where they are polarized in different planes. Because transmitted beams which are polarized in different planes, even though they occupy the same frequency band, may transmitted substantially free from interference, a receiver may separate the transmitted beams using a corresponding polarized antenna. In the past, however, polarizers for satellite antenna have been heavy, bulky, and structurally complex devices.
A need has long existed in the industry for light weight parallel plate polarizers suitable for use with satellite antennas.